FIG. 1 illustrates a conventional UV light emitting diode (UV LED) that includes an epitaxial substrate 11, an active layer 12 which is disposed on the epitaxial substrate 11, a transparent conducting layer 14 which is disposed on the active layer 12, and an electrode unit 15 which transmits an external energy to the active layer 12. When the external energy is transmitted into the active layer 12, the active layer 12 generates UV light.
The epitaxial substrate 11 is made from sapphire. The active layer 12 includes a quantum well structure having alternately disposed AlGaN layers and GaN layers. The transparent conducting layer 14 is made from a material with low contact resistance and high transmittance.
The structure of the UV LED is similar to that of a blue LED. Both the blue LED and the UV LED have the same drawbacks, such as heat dissipation problem, current spreading problem, or epitaxial mismatching problem. Because the wavelength of the UV LED is smaller than that of the blue LED, the current spreading problem of the UV LED is much worse than that of the blue LED.
In order to solve the current spreading problem of the UV LED, a current spreading layer (not shown) may be included in the aforementioned UV LED. The current spreading layer is usually made from Ga2O3:Zn (ZGO). However, since the current spreading layer has a work function smaller than that of the active layer 12, the current spreading layer cannot form an ohmic contact with the active layer 12.